1. Field of the Invention
This invention relates generally to methods for counting objects. More particularly, this invention relates to methods for counting objects arranged in a linear array or other predetermined pattern. Specifically, this invention relates to methods for counting integrated circuit chips contained in a shipping tube that is being conveyed.
2. Description of the Prior Art
In the semiconductor industry, integrated circuit chips ("IC chips") are commonly transported within a manufacturing facility or shipped to customers in elongated shipping tubes. The IC chips are typically positioned within the shipping tubes in a stacked or end to end sequence such that the front end of one IC chip abuts the back end of the next IC chip within the shipping tube.
In many cases, it may be desirable to count the number of IC chips in a shipping tube prior to delivering the shipping tube to a customer. The customer may also desire to count the number of IC chips in a shipping tube that it receives or one that is being used in manufacturing. One method for counting IC chips within a shipping tube is to manually count the IC chips. The manual counting process is, however, slow and subject to error. Another similar method is to visually count the IC chips within the shipping tube (which is typically comprised of a transparent or substantially transparent material). This method is also slow and generally subject to more error than the manual counting process.
Stationary photoelectric or inductive proximity sensor systems provide yet another method for counting the IC chips in a shipping tube. In these systems, the shipping tube containing IC chips is transported or conveyed through the detection zone of the particular sensor. As the shipping tube is conveyed through the detection zone, the sensor successively detects a particular discriminating aspect of each individual IC chip, thereby counting the IC chips as the shipping tube is transported. While this method is generally faster and less subject to error than the manual or visual counting methods, there are some limitations. Initially, because the sensors are stationary, the detection zone of the sensor will be a point on the particular transport means. Thus, to obtain a correct count, the particular discriminating aspect of each and every IC chip in the shipping tube must pass through this point on the transport means. Accordingly, transport apparatus, such as that disclosed in U.S. Pat. No. 5,041,721, must typically be used to ensure that the particular discriminating aspect of each and every IC chip within a shipping tube passes within the point detection zone of the stationary sensor. If such stationary sensor systems and the required transport apparatus are positioned in an X-Y plane, with the Y axis being the transport direction of the transport apparatus, and the point detection zone falling on the Y axis (i.e., the line wherein X is equal to 0), it is clear that a skew of the shipping tube relative to the Y axis may result in the particular discriminating aspect of one or more of the IC chips within the shipping tube not being transported through the point detection zone of the sensor. Additionally, transport apparatus, such as the apparatus disclosed in U.S. Pat. No. 5,041,721, are relatively expensive to construct. Furthermore, such transport apparatus may have little utility other than for use in a stationary sensor counting system. For example, the transport apparatus may be unusable as an apparatus to convey shipping tubes containing IC chips through an automated shipping tube packaging apparatus.
Thus, there exists a need for a method and apparatus for counting IC chips within a shipping tube, wherein the shipping tube may be transported on conventional transport apparatus, such as a conveyor belt, and wherein the shipping tube may be skewed with respect to the X and Y axis of the transport apparatus.